This invention relates to the field of pressure regulators that convert high-pressure gas in a cylinder to a substantially constant, lower output pressure or to a substantially constant output flow. In particular, this invention relates to piston regulators of the type that are arranged to seal on the low-pressure side of a valve seat.
Integrated regulators are mounted on high pressure cylinders and convert the 0-300+ bar pressure in the cylinder to a substantially constant lower pressure at the output. Depending on the application, the lower-pressure output may be delivered directly to a device using regulated pressure or it may be fed through a restriction to give a substantially constant flow, as used, for example in escape equipment or in medical oxygen therapy equipment.
A typical piston regulator includes a seal on a piston that is movable towards and away from a valve seat. When the seal is in contact with the seat, fluid flow from a pressurised source, such as a cylinder, to the outlet is prevented. If the valve is open on the other hand, fluid will flow at a rate determined by the degree of opening of the valve. The piston may be arranged to seal on the input (high pressure) or output (low pressure) side of the valve.
In many ways, the design of a piston regulator that seals on the low-pressure side is more straightforward. Essentially, such a regulator relies on a spring, or similar loading mechanism, to bias the piston in an open position relative to the seat. When the regulator is in use, the bias force provided by the spring is countered by a secondary pressure that pushes the piston towards the seat and that acts over a relatively large surface area. When the seat is sealed, the secondary pressure must supply sufficient force to seal the seat against primary pressure from the cylinder plus an additional force that overcomes the bias of the spring. If fluid is then withdrawn from the outlet for use, the secondary pressure falls, it becomes insufficient to seal the seat and the valve is opened to a degree that, ideally, matches the demand. The valve will remain open, allowing fluid to replenish from the cylinder at a rate to balance its removal, until fluid is no longer required. At this point the secondary pressure rises, until it again overcomes the bias of the spring and provides sufficient force to seal the seat.
Regulators that seal on the high-pressure side are generally of a more complex design, with more forces to balance. Their advantage is that the design tends to be more adaptable and, in particular, can be made such that the secondary pressure delivered to the output can be adjusted, according to requirements. As noted, the seal on this type of regulator is on the input (high pressure) side of the valve seat. Typically, also on the high-pressure side, is a sealing spring, which presses the seal into sealing contact with the seat. In order to open the valve, a diaphragm or piston, with significantly larger (typically over ten times) diameter than the seat, is located on the low pressure side and is pushed by a regulating spring onto a pin or shaft that extends through the seat to connect with the seal. The diaphragm or piston seals a chamber from which fluid at secondary pressure can be drawn through an output. Without any secondary pressure, the force from the regulating spring tending to open the valve will exceed the combined forces arising from the sealing spring and internal fluid pressure that act to close the valve. The pin or shaft will therefore be pushed further through the valve seat, opening the valve and allowing fluid to flow from the high-pressure side. Secondary pressure will then build up in the chamber sealed by the diaphragm (or piston). This pressure acts over the area of the diaphragm to move the diaphragm away from the shaft, which in turn is pushed upwards by the sealing spring and input pressure to seal the seat. If fluid is removed through the output on the low-pressure side, the secondary pressure falls, the force from the regulating spring pushes the diaphragm back onto the shaft, which in turn lifts the seal from the seat, ideally to a degree that matches the demand. Fluid flows through the valve until secondary pressure is built up to the level required to overcome the force of the regulating spring.
In order to vary the output pressure, and so to provide a variable-output regulator, the compression of the regulating spring is adjusted. The level to which secondary pressure is allowed to build up before the seal is re-seated is controlled primarily by the imbalance between the opposing force arising from the regulating and sealing springs and by the area of piston or diaphragm over which the secondary pressure acts. Of these factors, the most readily adjustable is the regulating spring force, as this spring is accessible on the low-pressure side of the regulator. Generally a handwheel with actuation means, most frequently a thread, is used to vary regulating spring compression. This accordingly controls the level of secondary pressure at the output.
It is not straightforward to construct a variable-output regulator that seals on the valve low-pressure side. The regulating spring is generally contained within the inner workings of the valve, making it far more difficult to access to adjust compression. This is to be contrasted with the above-described high-pressure-side arrangement in which the regulating spring is positioned above the piston or diaphragm that seals the secondary pressure chamber. It is possible to load the regulating piston on the low-pressure-side version with a spring that acts from outside the secondary pressure chamber. This however brings its own complications. These complications are identical to those that arise when implementing a particular method of shutting off the regulator valve, which will be explained below.
When a regulated cylinder is not being used, or, in particular, when it is in storage or in transport, it is of course highly desirable to be able to close the valve to prevent unintended operation. It is a serious disadvantage with a piston-type regulator that seals on the low pressure side that there is no satisfactory way in which effect such a closure.
The previously-described regulators that seal on the high-pressure side can be turned off simply by removing the regulating spring load. The sealing spring and input cylinder pressure then drive the seal against the seat, closing the valve. When pressure is turned off in this way, the regulated cylinder can be safely stored or transported.
In the alternative regulator structure, in which the seal is on the low-pressure side, it is impossible to adopt this approach. One option, which similarly exploits the fact that the high-pressure valve in the regulator may also be used to turn the gas pressure off, is to use a loading mechanism such as a screw or spring to load the piston such that it can be pressed on to the seat and directly seal the regulator. In this way, the piston acts with the seat to fulfil a dual purpose as both a regulator seal and an on/off valve. An example of the type of mechanism is disclosed in EP0459966—“Arrangement in gas regulator”.
There is however a fundamental problem with this approach.
The force required to compress the spring for regulator function is typically large compared to the force to seal the reducer seat. For example, on one regulator design, the spring might exert 300N, while the force on the seat required to effect a seal is about 30N.
The force that must be applied to the top of the piston, by means of the secondary pressure, is therefore quite significant. In this example, it needs to be 330N: 300N to overcome the spring plus 30N to provide sealing force.
Consider now, a piston-type regulator in which, as described above, a separate loading mechanism is included to close the valve for storage. In the event that the regulator needs to be switched off, the loading mechanism is activated to push the piston down to directly seal the seat. The closing mechanism must be able to close the valve independently of any regulating function that is being performed at the time. That is, it must seal the valve regardless of the level of secondary pressure that is already acting on the piston. If secondary pressure is minimal, with the valve fully open, then the closing force required to close the example considered here is, as before, 330N.
At the point that the force is applied to the piston to close the seat, the regulator may be open or closed and there may or may not be any secondary pressure in the low pressure area of the reducer.
If there is full secondary pressure in the low pressure area of the reducer and the seat is already in contact with the seal, the valve will already be closed. The closing mechanism is engineered to provide 330N, to guard against the scenario with minimal secondary pressure. If this pressure is then applied to the top of the piston, the load on the seal will be the existing sealing load of 30N (from the secondary pressure) plus 330N (from the closing mechanism). That is, 360N, or 12 times the force needed to effect a seal, will be applied to the materials of the seat and seal. This level of force is so far in excess of the usage force that it can easily result in damage to the seal. In consequence, the high-pressure regulator valve will no longer seal at the original 30N sealing force, harming the performance of the regulator and usually causing leakage at the original 30N force.
In its simplest form, this approach to switching off a regulator uses a screw that acts directly on the piston to seal the seat. It is almost impossible to judge what fraction of the 330N available needs to be applied to ensure that the regulator seat is closed, making it extremely likely that damage will occur. Attempts have been made to use springs to push the piston to take up tolerances and apply a more controlled load, but the fundamental problem of an excessive load on the seat whenever secondary pressure is present persists.
A similar problem is encountered in designing a variable-output version of the piston-type regulator. It is possible to load the regulating piston with a spring, which reduces the secondary pressure needed to reseal the valve. The force applied by the spring however must be effective regardless of the presence or absence of secondary pressure. If secondary pressure is present when spring load is applied, the seat will be overloaded and so liable to damage.
It would however be advantageous to be able to construct a variable-output regulator that seals on the low-pressure side. In considering the forces acting on the valve as it performs its regulator function, both low-pressure and high-pressure arrangements include a contribution from the high pressure gas inside the cylinder acting over the area of the seat. In the low-pressure construction, this force acts to open the valve; in the high-pressure construction, it acts to seal it. In both cases however, the size of its contribution is dependent on the pressure of gas in the cylinder. This is a variable factor that falls as the cylinder empties. It follows therefore that the accuracy with which regulator output pressure can be maintained over the full range of cylinder output pressures is crucially affected by such variation. For high-pressure regulators in which it is very desirable that the output pressure is maintained from a full to an empty cylinder, the high pressure gas acting on the seat determines the accuracy. The seat has to be large enough to pass the flow specified for the regulator at the lowest cylinder pressure. The high pressure on the seat area is most often the main variable. For optimum regulator accuracy therefore it is desirable to minimise the relative size of this force and one way to achieve this is to minimise the area of the seat.
By sealing the seat on the high-pressure side if the valve, it is not only necessary to have the seat large enough to pass the flow specified but also to allow a pin to extend through it to push down the seal. The pin forces the seat to be larger to compensate for the cross-sectional area it takes up. This means that the sealing area for the high pressure seat is larger than it has to be purely to pass the flow. The low-pressure construction has no need of the pin and so the seat—seal effective area is smaller. This reduces the effect of its variable contribution to regulator output pressure. For the same flow capacity therefore, it is possible to design a more accurate regulator that seals on the low-pressure side of the valve. The problem, of course, is that this is not straightforward to design and that the prior art has no satisfactory way in which to close it. For this reason, the design of regulator that seals on the high-pressure side is used when variable output is required, despite its reduced accuracy.
The diaphragm or piston can be made larger to mask the variations arising through seat area, but this makes the regulator bigger and more expensive, requiring a larger regulating spring.
A further advantage of sealing on the low-pressure side is that, if the seat leaks, the build up in secondary pressure increases the sealing load on the seat and therefore helps to seal the seat, preventing further escape of gas. By way of contrast, if the seat that is sealed on the high-pressure side leaks, the increase in output pressure does not result in an increase in sealing load on the seat.
It is, of course, possible to turn off a regulator that seals on the low-pressure side by some other mechanism that bypasses the requirement to push the piston seal down onto the seat. Two principal alternatives are known, but these possess their own disadvantages.
In one arrangement, a high pressure on/off valve is provided between the regulator and the cylinder. The high pressure valve isolates the cylinder supply from the regulator. This type of valve is very common: an example is disclosed in CA2178573—“valve and pressure regulator assembly for gas cylinder and gas cylinder comprising same”.
This arrangement suffers from a number of disadvantages. First, it requires a moving high pressure seal on the mechanism (usually a valve stem) to operate the on/off valve. Secondly, adiabatic heating occurs downstream of the on/off valve on opening. That is, the volume between valve and regulator is heated as a result of gas compression. The heating can be significant, and this volume can therefore be subjected to very high temperatures, which can potentially ignite the valve. Another risk of ignition arises again during opening, but this time as a result of rapid closure of the regulator valve as high-pressure gas first flows into the system and causes the secondary pressure to increase quickly. This closure results in rapid movement of the piston, causing the seat to impact the seal. Finally, providing a separate high-pressure valve represents a duplication of parts. The reducer already has a high-pressure seal and an on/off valve merely duplicates this functionality.
Alternatively, a low pressure valve may be provided downstream of the regulator. This enables the switching on and off to be effected at low pressure, which is technically far easier to achieve than switching at high pressure. In particular, material considerations are less restrictive. A valve that is closed using this arrangement is described in U.S. Pat. No. 6,273,130—“Gas regulator/valve device”.
This alternative arrangement though means that the number of seals that are pressurised, even when the valve is closed, is high. A leak in any one of these can cause the cylinder to drain during transport and storage. On the other hand, the adiabatic heating effect is eliminated The attendant difficulties of a high pressure on/off valve are eliminated or substantially reduced, as there is no immediate full opening of the high pressure seal.
The disadvantages of both these arrangements are avoided by direct sealing of the regulator seat by a seal on the piston.
There is therefore a perceived need for an alternative design of regulator that permits the potential advantages of a valve that is sealed on its low-pressure side to be realised, without running the risk of overloading and damaging the seat.
It is an object of this invention to provide a novel design of regulator that can be safely turned off, if required; that offers the potential for regulation with an adjustable output pressure, which can be maintained with improved accuracy in comparison with the prior art and that also includes a mechanism to protect the valve seat from overload.
The present invention relates to a novel design of regulator that is based on a regulator of the type that seals on the low-pressure side of the valve, but that can be turned off or adjusted to provide a variable output pressure without risk of overloading the valve seat.
The present invention provides a pressure reducing valve comprising:
a housing including a valve passage connected to a primary port and a secondary port;
a valve element provided in the housing, configured to adjust an opening degree of the valve passage by moving between a closed position in which a sealing part of the valve element is in contact with a valve seat and therefore closes the valve passage and an open position in which the valve element opens the valve passage, and configured to be pressed by secondary pressure toward the closed position;
a regulator biasing member configured to bias the valve element toward the open position against the secondary pressure;
an actuating mechanism that is operable to apply a shut-off force to the valve element to move it towards the closed position; wherein
the valve element is arranged such that, when the actuating mechanism is operated, a sealing force that arises between its sealing part and the valve seat is less than a total force arising through secondary pressure acting on the valve element and the shut-off force.
This invention is based on the realisation that it is possible to prevent or to negate the effect of secondary pressure as the valve is closed. The presence or absence of secondary pressure is a source of great uncertainty in determining the force necessary to close off the valve at its high pressure seat. By taking its effect out of the equation of forces acting to seal the valve, the valve can be turned off, without risk of overloading the seat.
In one implementation of this invention, the force applied to close off the valve is mediated by secondary pressure. This effectively cancels its contribution to the force on the seat. Specifically, in this embodiment, the present invention relates to a means of turning off the output pressure of a regulator, by applying load to a regulating valve element, such as a piston, using a closing piston, or similar, with a surface that is acted on by the secondary pressure to press it away from the regulating piston. The closing piston is movable between a first position in which it holds the regulating piston in its closed position and a second position in which the closing piston is moved away from the regulating piston, allowing the regulating piston freedom to move as it provides its normal regulator function.
When activating the loading mechanism to switch off the regulator, the high load required to overcome the regulator spring and to seal the seat is applied to the closing piston, which therefore moves towards the regulating piston. As in the prior art, there may or may not be any secondary pressure in this low pressure area when the regulator is switched off.
If there is secondary pressure in the low pressure area of the piston, this pressure acts equally on both the regulating piston and the closing piston to which the closing load is applied. The secondary pressure acting on the closing piston opposes the high closing load that is necessarily applied to switch off the regulator. The result is that the net force communicated from the closing piston to the regulating piston is reduced by the amount arising from the secondary pressure. If the secondary pressure is high, then this force will be small. The resultant force on the seal is therefore only slightly more than without the closing piston, which of course is only slightly more than that which is sufficient to effect the seal.
If there is no secondary pressure, the regulator valve is fully open and transmission of the full closing load through the closing piston to the regulating piston is necessary and occurs. The regulator spring takes up much of the force, and again only slightly more than sealing pressure is applied to the valve seat via the regulating piston.
This means that the presence or absence of secondary pressure in the regulator has almost no effect on the load being applied between seal and seat. The load on the high pressure seal is the same whether there is pressure in the low pressure area or not.
The present invention is not restricted by the mechanism employed to move the closing piston between the first position and the second position. Any conventional means may be used to effect the movement, such as a threaded hand-wheel, a lever that is movable between two positions, a toggle action mechanism, a cam, or any other mechanism.
The present invention may include a passage through the closing piston, with a moving seal of small area compared to the main diameter of the closing piston, to transmit fluid from a low pressure area, through the closing piston to a volume beyond it. The low pressure fluid, once in this volume, can be used for any function to which the output of a regulator is put. For example, metered through a metering orifice for delivery to a patient, or passed through a second reducer, which may be a precision reducer or a variable reducer to deliver a variable pressure, or any other function for which the output of a cylinder may normally be used.
The present invention may use the closing piston to relieve secondary pressure that is too high, for example such as may arise through a failure of the regulator seat. This can be achieved by locating vents in the bore above the normal retracted position of the closing piston, wherein increasing secondary pressure forces the closing piston upwards to expose the vents, allowing excess pressure to be relieved. Relative positioning can be arranged such that if the secondary pressure exceeds the normal operating pressure by a pre-set level, the vents to relieve the excess pressure are exposed.
In its second implementation, the present invention effectively splits the regulating piston into two parts. One part bears the secondary pressure load and any excess applied to close the valve; the other part, which includes the seal, is subject only to a load sufficient to effect the seal without damaging the seat.
The present invention therefore also includes a pressure reducing valve in which the valve element comprises a sealing element that incorporates the sealing part, a supporting element and a closing biasing member, the sealing element being slidable relative to the supporting element and biased by the closing biasing member against an upper surface of the supporting element and towards the seat such that:                in the absence of the shut-off force, the sealing and supporting element are moveable as a single unit under the influence of regulator biasing member and secondary pressure; and        in the event of operation of the actuation mechanism beyond a threshold level, the sealing element becomes moveable relative to the supporting element such that the influence of the shut-off force and secondary pressure is predominantly experienced by the supporting element, leaving the sealing element pressed onto the seat predominantly under the influence of the closing biasing member.        
In this way, the sealing part of the valve element is limited in the force with which is pushed against the seat by the load applied from the closing biasing member. This can be set so as to avoid damage to the seat. The unpredictable effect of secondary pressure is now directed through the supporting element, which is kept away from the valve seat.
In both implementations, the present invention allows closing of the regulating piston, without applying more than the intended load to the seat.
The present invention does not require a sliding high pressure seal between the high pressure area and the closing means.
The present invention avoids the need for a separate high pressure valve, as it makes use of the existing high pressure valve at the regulator seat. This makes it attractive as a solution for higher pressures, where avoiding sliding high pressure seals is an advantage.
As the sealing is at the regulator seat, it avoids the need for low pressure seals that would be pressurised during storage, solving the leakage problems associated with the second seal.
In its second implementation, the present invention allows output pressure to be adjusted by means of a variable load applied to the valve element in a direction counter to the influence of the regulator biasing member, the adjustable load being within a range of 0, through a level to balance the regulator biasing member to beyond the threshold level. Again, by separating the sealing part from the part of the valve element that is subject to regulating and closing forces, a variable output can be achieved in a valve that seals on its low pressure side. This therefore avoids the requirement of prior art variable-output regulators to have a shaft or pin extend through the valve seat. This means that the entire area of the valve seat is available for fluid flow, which allows the seat area to be smaller than known in the prior art, reducing the variable contribution to output pressure that arises from input pressure falling as the cylinder empties.
In another aspect, the present invention provides a regulating valve incorporating a primary valve seat and a stem attached to a valve element which is movable towards and away from the primary valve seat. The stem includes first and second conical portions, the second conical portion being of larger diameter and located a distance further from the primary valve seat. The primary valve seat includes a hole that is sealable by the first conical portion of the stem. The regulating valve also includes a passage extending from the primary valve seat to an opening in a chamber that contains the valve element, the passage being shorter than the distance between the conical portions of the valve stem, the first conical portion being located in this passage. The opening forms a secondary seat that is sealable by the second conical portion of the stem in the event of loss of the primary valve seat.
This aspect provides a new safety mechanism for a regulator valve. Without this design of valve stem, failure of the primary valve seat would result in loss of the seal and the full cylinder pressure would be communicated to the output, with possible catastrophic consequences. With this feature however, failure of the primary seat would result in the stem moving further into the passage and the larger conical portion would move to seal the secondary seat. This prevents full uncontrolled cylinder pressure being communicated to the output and allows the regulator to retain at least some regulating function. As failure of the primary seat is not an impossible event, for example if the cylinder contains oxygen, the valve may on occasion ignite and burn, this new feature represents an important development in the safety of regulators.
In order that the present invention may be well understood, embodiments thereof, which are given by way of example only, will now be described with reference to the accompanying drawings.